Refactor dashboard navigation, catalog grid, and API client

- Add sidebar dashboard navigation and support multiple dashboards
- Extract catalog grid/form logic to reusable CatalogsGrid component
- Add CatalogApiClient and DTOs for catalog CRUD operations
- Define dashboards with JSON data sources (Default, CatalogsGrid)
- Update configuration for dashboard and API endpoints
- Improve styling and imports for modularity and maintainability

DbFirst.BlazorWebApp/Components/Pages/Dashboard.razor

@@ -1,12 +1,87 @@
 @page "/dashboard"
+@page "/dashboards/{DashboardId?}"
 @inject Microsoft.Extensions.Configuration.IConfiguration Configuration
+@inject NavigationManager Navigation
 
-<DxDashboard Endpoint="@DashboardEndpoint" style="width: 100%; height: 800px;">
-</DxDashboard>
+<style>
+    .dashboard-shell {
+        display: flex;
+        gap: 0;
+        min-height: 800px;
+        border: 1px solid #e6e6e6;
+        border-radius: 6px;
+        overflow: hidden;
+        background: #fff;
+    }
+    .dashboard-nav {
+        width: 220px;
+        border-right: 1px solid #e6e6e6;
+        background: #fafafa;
+    }
+    .dashboard-nav-title {
+        padding: 0.75rem 1rem 0.5rem;
+        font-size: 0.7rem;
+        text-transform: uppercase;
+        letter-spacing: 0.08em;
+        color: #6c757d;
+        font-weight: 600;
+    }
+    .dashboard-nav-link {
+        display: block;
+        padding: 0.55rem 1rem;
+        color: inherit;
+        text-decoration: none;
+    }
+    .dashboard-nav-link.active {
+        background: #e9ecef;
+        font-weight: 600;
+    }
+    .dashboard-content {
+        flex: 1;
+        min-width: 0;
+        padding: 1rem;
+    }
+</style>
+
+<PageTitle>Dashboards</PageTitle>
+
+<div class="dashboard-shell">
+    <aside class="dashboard-nav">
+        <div class="dashboard-nav-title">Dashboards</div>
+        <NavLink class="dashboard-nav-link" href="dashboards/default">Default Dashboard (Designer)</NavLink>
+        <NavLink class="dashboard-nav-link" href="dashboards/catalog-grid">Catalogs (Dashboard Grid)</NavLink>
+        <NavLink class="dashboard-nav-link" href="dashboards/custom-grid">Catalogs (Custom Grid)</NavLink>
+    </aside>
+    <section class="dashboard-content">
+        @if (SelectedDashboardId == "default")
+        {
+            <DxDashboard Endpoint="@DashboardEndpoint" InitialDashboardId="DefaultDashboard" WorkingMode="WorkingMode.Designer" style="width: 100%; height: 800px;">
+            </DxDashboard>
+        }
+        else if (SelectedDashboardId == "catalog-grid")
+        {
+            <DxDashboard Endpoint="@DashboardEndpoint" InitialDashboardId="CatalogsGrid" WorkingMode="WorkingMode.ViewerOnly" style="width: 100%; height: 800px;">
+            </DxDashboard>
+        }
+        else if (SelectedDashboardId == "custom-grid")
+        {
+            <h3>Catalogs (Custom Grid)</h3>
+            <CatalogsGrid />
+        }
+    </section>
+</div>
 
 @code {
-    private string DashboardEndpoint => $"{Configuration["ApiBaseUrl"]?.TrimEnd('/')}/api/dashboard";
-}
+    [Parameter] public string? DashboardId { get; set; }
 
-@* <DxDashboard Endpoint="api/dashboard" WorkingMode="WorkingMode.ViewerOnly" style="width: 100%; height: 800px;">
-</DxDashboard> *@
+    private string DashboardEndpoint => $"{Configuration["ApiBaseUrl"]?.TrimEnd('/')}/api/dashboard";
+    private string SelectedDashboardId => string.IsNullOrWhiteSpace(DashboardId) ? "default" : DashboardId;
+
+    protected override void OnParametersSet()
+    {
+        if (string.IsNullOrWhiteSpace(DashboardId))
+        {
+            Navigation.NavigateTo("dashboards/default", replace: true);
+        }
+    }
+}